1. Field of the Invention
The present invention relates to an image capture apparatus and zoom lens, and more particularly o a zoom lens having an optical-axis folding means and an image capture apparatus using such a zoom lens, and to techniques capable of compatibly realizing an increase in the size of an imager device of a digital camera and a reduction in the thickness of the digital camera.
2. Description of Related Art
In recent years, digital cameras have exceeded film cameras in annual sales and have spread at a remarkable pace. Commercially popular types of digital cameras, particularly so-called digital compact cameras, are small-sized, lightweight, and low in running cost compared to compact film cameras and allow users to confirm captured results on their liquid crystal display screens immediately after each image capture. This is considered to be the reason why digital compact cameras have spread.
A critical issue to the miniaturization of a compact digital camera particularly resides in the thickness of the lens used, and a large number of digital cameras adopt a telescopic lens barrel, called a retractable lens, which when not used can be accommodated in a camera in a compact, collapsed state. However, such a retractable lens has the large disadvantage of being easily damaged by the shock of an external force.
As opposed to the retractable lens, there is a thin-type compact digital camera whose thinness is realized by providing an optical-axis folding member in the lens system as shock-resistant means which enables a reduction in the thickness of the camera, as disclosed in Japanese Patent Application Publication Number 2004-354869 (Patent Literature 1), Japanese Patent Application Publication Number 2004-193848 (Patent Literature 2) and Japanese Patent Application Publication Number 2004-170707 (Patent Literature 3). Such a so-called folding optical system can achieve a reduction in the thickness of the camera, but it needs a space in which to arrange reflection members such as a prism and a mirror. In addition, the reflection members do not contribute to a zooming function or an image forming function in the zoom lens, and they occupy an originally unnecessary space in the zoom lens. As a result, the reflection members invite an increase in the volume of the lens and hinder the miniaturization of the camera. For this reason, in the field of compact digital cameras which adopts folding optical systems; the miniaturization of cameras has been achieved by adopting imager devices of a small screen size.
However, if the screen size of an imager device is made small with the number of effective pixels capable of ensuring high resolution maintained, the pixel pitch becomes fine and the area of one pixel of a sensor for photoelectric conversion becomes so small as to invite a decrease in sensitivity and an increase in noise. As a result, this construction tends to easily cause noticeable losses of highlight details in bright subjects and noticeable losses of shadow details in dark subjects, and it is unfavorable to the retractable lens in terms of image quality.
In addition, even if the miniaturization of a lens is achieved by adopting a small-sized imager device, the outside dimension of the package of the imager device is considerably large compared to its effective screen size, so that the thickness of a camera is restricted by the package size and the extent of reduction of the thickness is limited.
Although the compact digital cameras pursue miniaturization by combining small-sized imager devices with retractable lenses or folding lenses, digital cameras of high image quality are designed to meet demands for higher image quality. The digital cameras of high image quality can suppress the occurrence of noise even in the case of a high sensitivity setting and can readily avoid losses of highlight details and shadow details owing to their wide range of grayscale representation and can attain high resolution, by adopting large-sized imager devices, such as 35 mm full size devices or so-called APS-C size devices. Such a digital camera is marketed as a single-lens reflex or range finder type of camera which uses interchangeable lenses, and it is incomparably larger in volume and weight than compact digital cameras are. The depthwise dimension of the digital camera in particular becomes so large as to remarkably impair portability, even when a zoom lens having a zoom ratio of the order of 3 and approximately equal to the average zoom ratio of compact digital cameras is attached.